Method of manufacturing an image sensor by joining a pixel circuit substrate and a logic circuit substrate and thereafter thinning the pixel circuit substrate

ABSTRACT

The present technology includes: bonding a device formation side of a first substrate having a first device and a device formation side of a second substrate having a second device in opposition to each other; forming a protective film on at least an edge of the second substrate having the second device; and reducing a thickness of the first substrate.

TECHNICAL FIELD

The present disclosure relates to a method of manufacturing asemiconductor device having a structure for bonding a plurality ofsubstrates.

BACKGROUND ART

High integration of a semiconductor device has been achieved by adoptionof the fine process and improvement of the mounting density in atwo-dimensional LSI (Large-Scale Integration). In recent years, however,physical limitations of the microfabrication have come within sight, anda three-dimensional LSI has drawn the attention.

In the three-dimensional LSI, a semiconductor device is formed in such amanner that substrates on which devices having various functions (forexample, a memory device, a logic device, and an image sensor device)are formed are bonded with each other, and thereafter an upper-layersubstrate is thinned down to a desired thickness using a grindingprocess (for example, see Japanese Unexamined Patent ApplicationPublication No. 2011-96851 (PTL 1)).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2011-96851

SUMMARY OF THE INVENTION

In the three-dimensional LSI, however, it is more likely that alower-layer substrate will be damaged in reducing the thickness asdescribed above. This is because an edge of an upper-layer substratethat is processed by the grinding in an acute-angled shape and that iscalled a knife edge as we say is unendurable against a stress to beexerted thereon, and cracking or peel-off occurs. Broken pieces of theknife edge that arise from this cracking or peel-off strike on thesurface of the lower-layer substrate to damage wiring and the like thatare formed on the lower-layer substrate. For such a reason, there hasbeen an issue that the reliability and manufacturing yield of asemiconductor device could be deteriorated.

Accordingly, it is desirable to provide a method of manufacturing asemiconductor device that allows the reliability and manufacturing yieldof a semiconductor device to be improved.

A first method of manufacturing a semiconductor device according to anembodiment of the present disclosure includes the following steps (A1)to (C1):

(A1) Bonding a device formation side of a first substrate having a firstdevice and a device formation side of a second substrate having a seconddevice in opposition to each other;

(B1) Forming a protective film on at least an edge of the secondsubstrate having the second device; and

(C1) Reducing a thickness of the first substrate.

In the first method of manufacturing a semiconductor device according toan embodiment of the present disclosure, the protective film is formedat the edge of the lower-layer substrate (first substrate), andthereafter a thickness of the upper-layer substrate (second substrate)is reduced. Therefore, occurrence of a damage of the lower-layersubstrate in reducing the thickness of the upper-layer substrate isreduced.

A second method of manufacturing a semiconductor device according to anembodiment of the present disclosure includes the following steps (A2)to (D2):

(A2) Forming a thinned portion at an edge of a first substrate having afirst device;

(B2) Forming a protective film that absorbs no laser beams on at leastan edge of a second substrate having a second device;

(C2) Bonding the second substrate and the first substrate with thesecond device and the first device opposed to each other; and

(D2) Selectively removing the thinned portion of the first substrateusing a laser.

In the second method of manufacturing a semiconductor device accordingto an embodiment of the present disclosure, the protective film thatabsorbs no laser beams is formed at the edge of the lower-layersubstrate (second substrate), the thinned portion is formed at the edgeof the upper-layer substrate (first substrate), and the edge of theupper-layer substrate is removed. Therefore, occurrence of a damage ofthe lower-layer substrate in removing the edge of the upper-layersubstrate is reduced.

A third method of manufacturing a semiconductor device according to anembodiment of the present disclosure includes the following steps (A3)to (C3):

(A3) Bonding a first substrate having a first device and a secondsubstrate having a second device with the first device and the seconddevice opposed to each other;

(B3) Reducing a thickness of an internal region excluding an edge of thefirst substrate; and

(C3) Removing the edge of the first substrate.

In the third method of manufacturing a semiconductor device according toan embodiment of the present disclosure, in a thinning process of theupper-layer substrate (first substrate), the internal region excludingthe edge of the upper-layer substrate is reduced in thickness, andthereafter the edge of the upper-layer substrate is removed. Therefore,occurrence of a damage of the lower-layer substrate in removing the edgeof the upper-layer substrate is reduced.

According to the first method of manufacturing a semiconductor device ofan embodiment of the present disclosure, the protective film is formedat the edge of the lower-layer substrate, and thereafter a thickness ofthe upper-layer substrate is reduced. Therefore, it is possible toreduce the thickness of the upper-layer substrate without damaging thelower-layer substrate.

According to the second method of manufacturing a semiconductor deviceof an embodiment of the present disclosure, the protective film thatabsorbs no laser beams is formed at the edge of the lower-layersubstrate, and the thinned portion is formed at the edge of theupper-layer substrate. Therefore, it is possible to remove the edge ofthe upper-layer substrate without damaging the lower-layer substrate.

According to the third method of manufacturing a semiconductor device ofan embodiment of the present disclosure, the internal region excludingthe edge of the upper-layer substrate is reduced in thickness, andthereafter the edge of the upper-layer substrate is removed. Therefore,it is possible to remove the edge of the upper-layer substrate withoutdamaging the lower-layer substrate.

In the first to third methods of manufacturing a semiconductor deviceaccording to the above-described respective embodiments of the presentdisclosure, it is possible to improve the reliability and manufacturingyield of a semiconductor device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram showing a configuration of an imagepickup device according to any of first to fourth embodiments of thepresent disclosure.

FIG. 2 is a simplified configuration diagram of the image pickup deviceillustrated in FIG. 1.

FIG. 3 is a simplified configuration diagram of an existing image pickupdevice.

FIG. 4 is a cross-sectional view of the image pickup device illustratedin FIG. 1.

FIG. 5A is a schematic process diagram showing a method of manufacturinga semiconductor device according to a first embodiment of the presentdisclosure.

FIG. 5B is a schematic process diagram showing a process following onthe process shown in FIG. 5A.

FIG. 5C is a schematic process diagram showing a process following onthe process shown in FIG. 5B.

FIG. 6A is a schematic process diagram showing another example of themethod of manufacturing a semiconductor device according to the firstembodiment of the present disclosure.

FIG. 6B is a schematic process diagram showing a process following onthe process shown in FIG. 6A.

FIG. 6C is a schematic process diagram showing a process following onthe process shown in FIG. 6B.

FIG. 7A is a schematic process diagram showing a method of manufacturinga semiconductor device according to a second embodiment of the presentdisclosure.

FIG. 7B is a schematic process diagram showing a process following onthe process shown in FIG. 7A.

FIG. 7C is a schematic process diagram showing a process following onthe process shown in FIG. 7B.

FIG. 7D is a schematic process diagram showing a process following onthe process shown in FIG. 7C.

FIG. 8A is a schematic process diagram showing a method of manufacturinga semiconductor device according to a third embodiment of the presentdisclosure.

FIG. 8B is a schematic process diagram showing a process following onthe process shown in FIG. 8A.

FIG. 8C is a schematic process diagram showing a process following onthe process shown in FIG. 8B.

FIG. 9A is a schematic process diagram showing a method of manufacturinga semiconductor device according to a fourth embodiment of the presentdisclosure.

FIG. 9B is a schematic process diagram showing a process following onthe process shown in FIG. 9A.

FIG. 9C is a schematic process diagram showing a process following onthe process shown in FIG. 9B.

FIG. 10 is a schematic block diagram of an electronic apparatus (camera)according to an application example.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, some embodiments of the present disclosure are describedwith reference to the drawings. It is to be noted that the descriptionsare provided in the order given below.

1. Configuration of Image Pickup Device

2. First Embodiment (a method in which a protective film is formed on alower-layer substrate, and thereafter a thinning process is carried out)

3. Second Embodiment (a method in which a lower-layer substrate isprocessed prior to bonding)

4. Third Embodiment (a method in which a thinned portion of anupper-layer substrate is removed using a laser)

5. Fourth Embodiment (a method in which a device formation region of anupper-layer substrate is reduced in thickness, and thereafter an edge ofthe upper-layer substrate is removed)

6. Application Examples (examples of an electronic apparatus)

1. Configuration of Image Pickup Device

FIG. 1 shows an overall configuration of a MOS solid-state image pickupdevice (image pickup device 1) to which a semiconductor device accordingto any of first to fourth embodiments of the present disclosure to behereinafter described is applied. This image pickup device 1 is an imagepickup device suitable for photographing color images (still images ormoving images), and is configured of a pixel region 3 (so-called pixelarray) and a peripheral region 4. The pixel region 3 is configured insuch a manner that a plurality of pixels 2 each of which includes aphotoelectric conversion section are arrayed in a matrix pattern on asubstrate.

The pixel 2 that is provided at the pixel region 3 includes a photodiodePD that serves as the photoelectric conversion section, a plurality ofpixel transistors Tr (MOS transistors), and the like. The plurality ofpixel transistors Tr may be, for example, three types of transistors ofa transfer transistor, a reset transistor, and an amplifying transistor,or may be alternatively configured of four types of transistors byadding a selection transistor. It is to be noted that an equivalentcircuit of a unit pixel is similar to a typical equivalent circuit, andthus detailed description thereof is omitted. The pixel 2 isconfigurable as a single unit pixel. However, the pixel 2 may beconfigured in a pixel sharing structure. This pixel sharing structure issuch that the plurality of photodiodes PD share a floating diffusionconfiguring the transfer transistor, and any of transistors other thanthe transfer transistor.

At the peripheral region 4, there are provided a control circuit 5, avertical driving circuit 6, a column signal processing circuit 7, ahorizontal driving circuit 8, an output circuit 9, and the like.

The control circuit 5 receives an input clock, and data commandingoperation modes and the like, and outputs data such as internalinformation of the image pickup device 1. More specifically, thiscontrol circuit 5 generates a clock signal and a control signal thatserve as reference signals for operation of the vertical driving circuit6, the column signal processing circuit 7, the horizontal drivingcircuit 8, and the like on the basis of a vertical synchronizationsignal, a horizontal synchronization signal, and a master clock.Further, the control circuit 5 inputs these clock signal and controlsignal to the vertical driving circuit 6, the column signal processingcircuit 7, the horizontal driving circuit 8, and the like.

The vertical driving circuit 6 may be configured of, for example, ashift register. This vertical driving circuit 6 selects a pixel drivewiring, and provides pulses for driving the pixels to the selected pixeldrive wiring to drive the pixels on each row basis. More specifically,the vertical driving circuit 6 performs a selective scanning for each ofthe pixels 2 at the pixel region 3 sequentially in a vertical directionon each row basis, and provides a pixel signal based on a signal chargethat is generated in accordance with the light-receiving amount in thephotodiode PD on each of the pixels 2 to the column signal processingcircuit 7 through a vertical signal line 9.

The column signal processing circuit 7 may be, for example, arranged foreach column of the pixels 2, and performs signal processing operationsuch as noise rejection for signals to be output from the pixels 2 in asingle row for each of the pixel columns. More specifically, the columnsignal processing circuit 7 carries out a signal processing operationsuch as CDS for rejecting a fixed pattern noise inherent in the pixel 2,signal amplification, and analog-to-digital conversion. At an outputstage of this column signal processing circuit 7, a horizontal selectionswitch (not shown in the drawing) is provided to be connected between ahorizontal signal line 10.

The horizontal driving circuit 8 may be configured of, for example, ashift register, and selects each of the column signal processingcircuits 7 in order by outputting horizontal scan pulses sequentially todrive each of the column signal processing circuits 7 to output a pixelsignal to the horizontal signal line 10.

The output circuit 9 performs a signal processing operation for signalsto be provided sequentially from each of the column signal processingcircuits 7 through the horizontal signal line 10 to output the resultantsignals. In some cases, for example, this output circuit 9 may performonly buffering, or may perform black level adjustment, correction ofcolumn variations, various digital signal processing operations, and thelike. Input/output terminals 12 deal with signal handling among externalcircuits.

Each of FIGS. 2 (A) and 2 (B) shows a simplified configuration of theimage pickup device 1 to which a semiconductor device according to anyof the first to fourth embodiments of the present disclosure is applied,and FIG. 3 shows a simplified configuration of an existing MOSsolid-state image pickup device (image pickup device 100).

In the currently available image pickup device 100, as shown in FIG. 3,a pixel section 102A, a control section 102B, and a logic circuit LC forsignal processing are formed in a single semiconductor substrate 110.Typically, an image sensor 110 is configured of a pixel region 113 and acontrol circuit 115.

On the contrary, in the image pickup device 1 to which a semiconductordevice according to any of the first to fourth embodiments of thepresent disclosure is applied, as shown in FIG. 2 (A), a pixel section2A, a control section 2B, and a logic circuit LC are formed on twoseparate substrates (for example, a first semiconductor substrate 10Aand a second semiconductor substrate 10B). More specifically, the imagepickup device 1 has a configuration in which the pixel section 2A andthe control section 2B are formed on the first semiconductor substrate10A, while the logic circuit LC including a signal processing circuitfor performing the signal processing operation is formed on the secondsemiconductor substrate 10B, and the first semiconductor substrate 10Aand the second semiconductor substrate 10B are electrically connectedwith each other.

It is to be noted that a combination of the pixel section 2A, thecontrol section 2B, and the logic circuit LC that are formed separatelyon the first semiconductor substrate 10A and the second semiconductorsubstrate 10B is not limited specifically, and for example, as shown inFIG. 2 (B), the pixel section 2A may be formed on the firstsemiconductor substrate 10A, and the control section 2B and the logiccircuit LC may be formed on the second semiconductor substrate 10Balternatively.

FIG. 4 shows a part of a cross-sectional configuration of the imagepickup device 1 on the basis of the configuration illustrated in FIG. 2(A). In this image pickup device 1, the first semiconductor substrate10A on which the pixel section 102A and the control section 102B areformed and the second semiconductor substrate 10B on which the logiccircuit LC is formed are stacked vertically with electrically connectedwith each other.

More specifically, this image pickup device 1 is configured (layeredproduct 10, see FIG. 4) to stack the first semiconductor substrate 10Aand the second semiconductor substrate 10B with the second semiconductorsubstrate 10B placed on the downside by bonding device formation sides(device layers 16A and 16B) on which the MOS transistors Tr are formedon the second semiconductor substrate 10B and the first semiconductorsubstrate 10A in opposition to each other. In this image pickup device1, the photodiode PD that serves as the photoelectric conversion sectionis arranged on the side of a surface (topside surface in the drawing,and hereinafter referred to as a backside) on the first semiconductorsubstrate 10A side. On junction surfaces of the first semiconductorsubstrate 10A and the second semiconductor substrate 10B, insulatinglayers 13A and 13B are formed on which multilayer wiring layers 14A and14B are formed, respectively.

It is to be noted that each of the MOS transistors Tr that are providedon the pixel section 2A and the control section 2B in the pixel region 3has a configuration in which a gate electrode is formed on a pair of asource electrode and a drain electrode with a gate insulating film inbetween (these component parts are not shown in the drawing). Further,on the backside of the first semiconductor substrate 10A, for example,an antireflective film 18, an insulating film 19 including alight-blocking film 19A, and a planarizing film 20 may be formed. At aposition corresponding to the photodiode PD on each of the pixels 2 onthe planarizing film 20, an on-chip lens 22 is provided with a colorfilter in between.

In the image pickup device 1 having such a configuration, the photodiodePD is irradiated with light via the on-chip lens from the backside ofthe first semiconductor substrate 10A, and a signal charge is generatedfor each of the pixels 2. It is possible to obtain image data by readingimage signals in all of the pixels 2 as voltage signals corresponding tothe amount of such a signal charge, for example. Hereinafter, thedescription is provided on an example of a method of manufacturing theimage pickup device 1.

(Manufacturing Method)

(Fabrication of First Semiconductor Substrate (First Substrate) 10A)

First, an image sensor, that is, the pixel section 2A and the controlsection 2B are formed in a device formation region on a substrate 11A.More specifically, in the pixel section 2A, for example, the photodiodePD that serves as the photoelectric conversion section in each of thepixels 2 is formed on the substrate 11A, and thereafter each of thepixel transistors Tr is formed. Here, a pixel transistor Tr adjacent tothe photodiode PD corresponds to the transfer transistor, and asource-drain region thereof (not shown in the drawing) corresponds to afloating diffusion FD. Further, the MOS transistors Tr are formed in thecontrol section 2B. Each of the MOS transistors Tr may be configured of,for example, a pair of n-type source/drain region, and the gateelectrode that is formed with the gate insulating film in between (thesecomponent parts are not shown in the drawing).

Next, after the insulating film 13A is formed on the substrate 11A,connection holes 15A are formed, and connecting conductors 15 to beconnected with a predetermined transistor are formed. Subsequently, ametallic layer that may be configured of multi-layered, for example,three-layer copper and the like is formed as a wiring layer 14A toconnect each of the connecting conductors 15. The steps described thusfar form the first semiconductor substrate 10A having the pixel section2A and the control section 2B thereon.

(Fabrication of Second Semiconductor Substrate (Second Substrate) 10B)

Next, the logic circuit LC including the column signal processingcircuit 7 and the like for the signal processing purpose is formed in adevice formation region on a substrate 11B. More specifically, forexample, the plurality of MOS transistors Tr configuring the logiccircuit LC are formed on the substrate 11B. Each of the MOS transistorsTr may be configured of, for example, a pair of n-type source/drainregion, and the gate electrode that is formed with the gate insulatingfilm in between (these component parts are not shown in the drawing).

Subsequently, in the same manner as is the case in the above-describedfirst semiconductor substrate 10A, the insulating layer 13B, theconnection holes 15A, the connecting conductors 15, and a wiring layer14B are formed on the substrate 11B. The steps described thus far formthe second semiconductor substrate 10B having the logic circuit LCthereon. It is to be noted that, on top of the wiring layer 14B, astress correction film (not shown in the drawing) may be formed foralleviating a stress at the time of bonding of the first semiconductorsubstrate 10A and the second semiconductor substrate 10B to behereinafter described. The stress correction film may be configured insuch a manner that, for example, a P—SiN film (plasma nitride film) or aP—SiON film (plasma oxynitride film) may be formed in a film thicknesswithin a range of about 100 to 200 nm, for example.

(Bonding of First Semiconductor Substrate 10A and Second SemiconductorSubstrate 10B)

Next, the first semiconductor substrate 10A and the second semiconductorsubstrate 10B are bonded with the wiring layers 14A and 14B opposed toeach other. More specifically, for example, an adhesive material layer(not shown in the drawing) may be formed on one side of a junctionsurface of the first semiconductor substrate 10A or the secondsemiconductor substrate 10B, and the first semiconductor substrate 10Aand the second semiconductor substrate 10B are bonded with this adhesivematerial layer in between. Here, the bonding is performed with the firstsemiconductor substrate 10A on which the pixel region 3 is formed placedon an upper layer and with the second semiconductor substrate 10B placedon a lower layer.

It is to be noted that, for the bonding of the first semiconductorsubstrate 10A and the second semiconductor substrate 10B, plasma bondingmay be used apart from the bonding by the use of the above-describedadhesive material layer. In a case of the use of the plasma bonding,plasma SiO₂, SiN, SiC, or SiCN films, and the like are formed on each ofthe junction surfaces of the first semiconductor substrate 10A and thesecond semiconductor substrate 10B. The first semiconductor substrate10A and the second semiconductor substrate 10B are bonded with eachother in such a manner that a plasma treatment is performed for each ofthe junction surfaces on which these films are formed to be overlappedwith each other, and thereafter an annealing treatment is performed forthe overlapped junction surfaces. Here, the annealing treatment may bepreferably carried out in a low-temperature process at temperature of400 degrees centigrade or less that has no influence on the wiring andthe like.

(Reduction of Thickness of First Semiconductor Substrate 10A)

Subsequently, the backside (the substrate 11A side) of the firstsemiconductor substrate 10A is ground and polished to reduce a thicknessof the first semiconductor substrate 10A. More specifically, such areduction in thickness is carried out in such a manner that thesubstrate 11A having a thickness of about 600 μm, for example, may bereduced down to a thickness within a range of about 3 to 6 μm to facethe photodiodes PD with one another. By reducing the thickness of thefirst semiconductor substrate 10A, the backside of the firstsemiconductor substrate 10A serves as a light incidence surface in theimage pickup device 1 of a backside illumination type.

Finally, the antireflective film 18, the insulating film 19 includingthe light-blocking film 19A, and the planarizing film 20 are formed onthe backside of the first semiconductor substrate 10A. Further, thecolor filters 21 of red (R), green (G), and blue (B) corresponding toeach of the pixels, and the on-chip lens 22 are formed on thisplanarizing film 20, thereby bringing the image pickup device 1 tocompletion.

Hereinafter, as the methods of manufacturing a semiconductor deviceaccording to the first to fourth embodiments of the present disclosure,the description is provided on a method of reducing a thickness of thefirst semiconductor substrate 10A. It is to be noted that any componentparts essentially same as those of the above-described image pickupdevice 1 are denoted with the same reference numerals, and the relateddescriptions are omitted as appropriate.

2. First Embodiment

Each of FIG. 5A to FIG. 5C shows a method of manufacturing asemiconductor device according to a first embodiment of the presentdisclosure, in particular, a process of reducing a thickness of thefirst semiconductor substrate 10A.

In this embodiment, in the beginning, as shown in FIG. 5A, an edge ofthe first semiconductor substrate 10A is removed in a range of, forexample, a width of 2 mm and a depth of 100 μm to form a thinned portion31. Next, the first semiconductor substrate 10A and the secondsemiconductor substrate 10B are bonded with each other using, forexample, the above-described plasma bonding or other methods.

Subsequently, as shown in FIG. 5B, the first semiconductor substrate 10Ais ground to reduce the thickness of the whole surface of the substratein a mechanical manner, and thereafter an SiN film (protective film 32)with a film thickness of 3 μm, for example, is formed on the sidesurface of the first semiconductor substrate 10A and on the surface ofthe second semiconductor substrate 10B using, for example, an ion beammethod (see Japanese Unexamined Patent Application Publication No.2010-70788). In the event that broken pieces of the substrate 11A stickon the surface of the second semiconductor substrate 10B at the time ofgrinding of the first semiconductor substrate 10A, this protective film32 serves to cover the surface of the second semiconductor substrate 10Bincluding these broken pieces.

As a constituent material for this protective film 32, the use of amaterial may be preferable that has resistance to chemical liquid (forexample, acid-based chemical liquid) that is used in a chemical liquidtreatment for the backside of the first semiconductor substrate 10A tobe performed later. Specific examples of the material may include plasmaSiN, SiC, and SiCN films, and the like.

Thereafter, as shown in FIG. 5C, the surface of the substrate 11A issmoothed and further reduced in thickness using the chemical liquidtreatment. On this occasion, when the protective film 32 is not formedat an edge of the second semiconductor substrate 10B, there will be aconcern about a possibility that chemical solution could be immersedinto a portion damaged by the substrate 11A to cause elution of ametallic material to be used for configuring the wiring layer 14B thatis formed at the edge of the second semiconductor substrate 10B,resulting in occurrence of contamination. On the other hand, in thisembodiment, after an edge (thinned portion 31) of the firstsemiconductor substrate 10A is removed, the protective film 32 is formedon the surface of the second semiconductor substrate 10B, and thus adamaged portion arising from collision of broken pieces is sealed by theprotective film 32. This prevents metallic contamination that may becaused by elution of the wiring layer 14B.

It is to be noted that, in this embodiment, the protective film 32 isformed after the thinned portion 31 of the first semiconductor substrate10A is removed and the whole surface of the substrate 11A is reduced inthickness. However, as shown in FIG. 6A, the protective film 32according to this embodiment may be alternatively formed at the edge ofthe second semiconductor substrate 10B prior to the bonding of the firstsemiconductor substrate 10A and the second semiconductor substrate 10B.Following the formation of the protective film 32, as shown in FIG. 6Band FIG. 6C, formation of the thinned portion 31 at the edge of thefirst semiconductor substrate 10A, grinding and thinning of thesubstrate 11A, as well as removal of the thinned portion 31 are carriedout. Further, a method of forming the protective film 32 is not limitedspecifically so long as such a method allows the protective film 32 tobe formed locally at the edge of the second semiconductor substrate 10B.An example of such a method may include a chemical vapor phasefilm-forming method that blows local plasma and film-forming gas to theedge. As an alternative, a method of using a coater capable ofperforming a film formation only within a predetermined range byinjecting a coating film liquid from a narrow nozzle, and a method offorming the protective film only at the edge in such a manner thatcoating liquid or photoresist is coated over the whole surface, andthereafter lithographic exposure and removal of resist are performed maybe used.

In a currently-available thinning process, a grinder process is carriedout in the beginning. In grinding an upper-layer substrate using thisgrinder process, because this is a mechanical grinding, there is aconcern about a possibility that cracking or peel-off will occur at anedge of the upper-layer substrate as previously described. This crackingor peel-off of the upper-layer substrate strikes directly on an edge ofa lower-layer substrate as broken pieces to cause damage to the surfaceof the lower-layer substrate. When the wiring layer is formed on such adamaged portion, wires are exposed, and contamination may occur that iscaused by elution of metals to be used for configuring wires in athinning process using a wet etching and the like to be performedsubsequently. Also, even when the wiring layer is not formed on thelower-layer substrate, damage arising on the lower-layer substrate maycause dust generation, and this will pose an issue of deterioration inthe manufacturing yield.

As a method of solving such an issue, for example, Japanese UnexaminedPatent Application Publication No. 2003-15193 has disclosed a method inwhich grinding on the side of an SOI that serves as an active siliconlayer is interrupted halfway, and a substrate is removed as deep as apredetermined thickness using a chemical liquid treatment. By the use ofthis method, the edge of the upper-layer substrate is also removed infurther thinning the upper-layer substrate using the chemical liquidtreatment.

However, this method presupposes that edges of the upper-layer substrateand the lower-layer substrate that are stacked vertically are bondedwith each other, and that an insulating film and the like on theupper-layer substrate side that remain behind at the edge are removablewith chemical liquid to be used in removing the upper-layer substrate.In a case of a stacked three-dimensional semiconductor device, a step ismade at an edge in fabricating a device, and thus edges are typicallyput in an unbonded state. Further, since an SiN film serving as aninsulating film that is formed on each layer of the device is notremovable with chemical liquid, this method has no function other thanonly generation of a dust source at the edge.

On the contrary, in this embodiment, prior to a thinning process of theupper-layer first semiconductor substrate 10A using a chemical liquidtreatment, the protective film 32 is formed at the edge of the secondsemiconductor substrate 10B. By forming this protective film 32, adamaged portion of the second semiconductor substrate 10B that may beproduced due to direct striking of broken pieces arising from thesubstrate 11A in mechanical grinding of the first semiconductorsubstrate 10A is covered, and etching of the second semiconductorsubstrate 10B that may be caused by the chemical liquid treatment to beperformed subsequently is prevented. Therefore, this preventscontamination due to metal elution or dust generation from a damagedportion of the second semiconductor substrate 10B.

As described above, according to the method of manufacturing asemiconductor device of this embodiment of the present disclosure, priorto the thinning process of the upper-layer first semiconductor substrate10A using the chemical liquid treatment, the protective film 32 isformed at the edge of the second semiconductor substrate 10B that maypossibly get a direct striking of broken pieces arising from thesubstrate 11A in the thinning process of the first semiconductorsubstrate 10A. This prevents etching of the second semiconductorsubstrate 10B that may be caused by the chemical liquid. Therefore, thisprevents contamination due to metal elution or dust generation from thesecond semiconductor substrate 10B side, and makes it possible toimprove the reliability and manufacturing yield of a semiconductordevice.

Further, in the method of manufacturing a semiconductor device accordingto this embodiment of the present disclosure, the protective film 32 isformed only at a desired portion of the second semiconductor substrate10B, and thus warpage of the second semiconductor substrate 10B that maybe caused by a stress of the protective film is suppressed, and handlingis made easy as compared with a case where the protective film is formedover a whole surface of the second semiconductor substrate 10B.

3. Second Embodiment

Each of FIG. 7A to FIG. 7D shows a method of manufacturing asemiconductor device according to a second embodiment of the presentdisclosure, in particular, a process of reducing a thickness of thefirst semiconductor substrate. The manufacturing method in thisembodiment of the present disclosure is different from the methodaccording to the above-described embodiment in that prior to the bondingof the first semiconductor substrate 10A and the second semiconductorsubstrate 10B, a thinned portion 33 is formed at an edge of the secondsemiconductor substrate 10B, more specifically, at a region on which awiring layer is formed, and a protective film 34 is formed over a wholesurface thereof.

First, the second semiconductor substrate 10B is formed, and thereafteras shown in FIG. 7A, an edge where the wiring layer 14 of the secondsemiconductor substrate 10B is formed is reduced in thickness using atrimming process to form the thinned portion 33. It is to be noted that,as a method of forming the thinned portion 33, any method other than thetrimming process may be used alternatively. For example, a method ofapplying a polishing process only for a predetermined range (the edge inthis case), or an etching process method using a dry or wet process maybe used.

Next, as shown in FIG. 7B, the protective film 34 is formed over thewhole surface of the second semiconductor substrate 10B, morespecifically, on the side surface and the surface of the thinned portionthat are exposed by the removal of a device formation surface. Thisprotective film 34 is formed with a thickness of 10 μm, for example,using a material similar to that used for the protective film 32 whichis formed in the above-described first embodiment, that is, any ofplasma SiN, SiC, SiCN films and the like which are materials havingresistance to the chemical liquid, such as acid-based chemical liquid(fluonitric acid-based wet etching liquid), for example, which is usedfor reducing the thickness of the first semiconductor substrate 10A. Itis to be noted that, as a method of forming the protective film 34,because the top surface, that is, the device formation surface of thesecond semiconductor substrate 10B after the film-forming process iscompleted becomes a bonding surface, the protective film 34 may bepreferably formed uniformly to avoid an adverse influence on thebonding. More specifically, the use of an ALD (Atomic Layer Deposition)method that is excellent in the film thickness controllability may bepreferable. Alternatively, a CVD (Chemical Vapor Deposition) method maybe used. When the CVD method and the like are to be used, the surfaceflatness may be preferably improved by the use of a CMP method and thelike after a film-forming process is completed.

Further, prior to the formation of the protective film 34, the surfaceof the second semiconductor substrate 10B may be preferably smoothed andcleaned using a wet process. More specifically, metal-based impuritiesto be attached when using the scrubber cleaning for removing dust on thesurface of the second semiconductor substrate 10B, or using a machiningprocess like a trimming process are removed. In concrete terms, it issupposed to carry out a cleaning process using acid-based chemicalliquid (for example, hydrofluoric acid hydrogen peroxide mixed solution(FPM)). This improves the adhesiveness of the protective film 34 to thesecond semiconductor substrate 10B and the film-forming performance ofthe protective film 34, as well as a protective capability against thechemical liquid to be used in reducing the thickness of the firstsemiconductor substrate 10A.

As described above, in this embodiment of the present disclosure, thefirst semiconductor substrate 10A and the second semiconductor substrate10B are bonded with each other after the thinned portion 33 is formed atthe edge of the second semiconductor substrate 10B, and the protectivefilm is formed to cover this thinned portion 33. Subsequently, the firstsemiconductor substrate 10A is reduced in thickness. As a result, aswith the above-described first embodiment, it is possible to preventoccurrence of contamination due to metal elution and dust generation atthe edge of the second semiconductor substrate 10B at the time ofreducing the thickness using the chemical liquid treatment.

4. Third Embodiment

Each of FIG. 8A to FIG. 8C shows a method of manufacturing asemiconductor device according to a third embodiment of the presentdisclosure, in particular, a process of reducing a thickness of thefirst semiconductor substrate 10A. The manufacturing method in thisembodiment of the present disclosure uses a laser microjet for removingan edge (thinned portion 31) of the first semiconductor substrate 10A.

First, as shown in FIG. 8A, an edge of the first semiconductor substrate10A is removed in a range of, for example, a width of 2 mm and a depthof 100 μm to form the thinned portion 31. The use of the laser microjetfor removal of this thinned portion 31 in conjunction with the formationof the thinned portion 31 makes it possible to suppress occurrence ofdamage in the second semiconductor substrate 10B. More specifically, avoid is provided between the first semiconductor substrate 10A and thesecond semiconductor substrate 10B by providing the thinned portion 31between the first semiconductor substrate 10A and the secondsemiconductor substrate 10B. Further, the laser microjet that propagateswater generates strongly spreading radiation flux once a laserwavelength runs through the first semiconductor substrate 10A, andbecomes unable to keep a strong energy obtained by reflecting laserbeams. As a result, it is possible to suppress damage of the secondsemiconductor substrate 10B that is caused by the laser.

Next, as shown in FIG. 8B, a protective film 35 is formed at the edge ofthe second semiconductor substrate 10B. This protective film 35 isformed with a thickness of 1 μm using a material that absorbs no laserbeams, more specifically, SiO₂ or SiN film, and the like. As a result, aprocess selection ratio at the time of a process for removing thethinned portion 31 of the first semiconductor substrate 10A using thelaser microjet to be carried out in the subsequent process is assured,and damage of the second semiconductor substrate 10B that is caused bythe laser beams is prevented by virtue of the combined effect obtainedby forming the above-described void.

Subsequently, the first semiconductor substrate 10A and the secondsemiconductor substrate 10B are bonded with each other using theaforementioned plasma bonding and the like, and thereafter the wholebackside of the first semiconductor substrate 10A is reduced inthickness using the chemical liquid treatment.

As a currently-available method of removing an edge of an upper-layersubstrate, as with this embodiment, a method of using laser beams hasbeen disclosed (for example, see Japanese Unexamined Patent ApplicationPublication No. 2006-108532). More specifically, for a stackedupper-layer substrate, a predetermined position thereof is irradiatedwith laser beams to remove an edge of the upper-layer substrate, andthereafter the upper-layer substrate is ground to reduce the thicknessthereof. In this method, because the edge of the upper-layer substrateis removed prior to grinding of the upper-layer substrate, a knife edgeis not formed. Therefore, it is possible to grind the upper-layersubstrate in a predetermined thickness without causing damage to thesurface of a lower-layer substrate at the time of grinding. However,typically a process by the use of laser beams has no selection ratio,and thus damage of the lower-layer substrate occurs at the same timethat the edge of the upper-layer substrate is removed. As a result, asis the case in a currently-available thinning process, contamination dueto metal elution or dust generation may occur. Further, a laser beam hasa short focal length, and thus it may be technically difficult toprocess the upper-layer substrate without any change. Even if theupper-layer substrate is allowed to be processed, the upper-layersubstrate has to be processed ten times or more while focusing laserbeams.

On the contrary, in this embodiment, after the thinned portion 31 isformed at the edge of the first semiconductor substrate 10A, and theprotective film 35 that absorbs no laser wavelength is provided at theedge of the second semiconductor substrate 10B, the edge of the firstsemiconductor substrate 10A is removed using laser beams. This makes itpossible to perform the process without causing damage to the secondsemiconductor substrate 10B due to the laser beams.

It is to be noted that here the protective film 35 against the laserbeams is formed only at the edge of the second semiconductor substrate10B, however, a method of forming the protective film 35 is not limitedthereto. As an alternative, the protective film 35 may be provided overthe whole surface of the second semiconductor substrate 10B prior to thebonding of the first semiconductor substrate 10A and the secondsemiconductor substrate 10B.

5. Fourth Embodiment

Each of FIG. 9A to FIG. 9C shows a method of manufacturing asemiconductor device according to a fourth embodiment of the presentdisclosure, in particular, a process of reducing a thickness of thefirst semiconductor substrate 10A. The manufacturing method in thisembodiment of the present disclosure grinds an internal region 10 a inwhich an edge is left as it is on the backside of the firstsemiconductor substrate 10A to reduce it as deep as a predeterminedthickness, and thereafter the edge is removed.

First, as shown in FIG. 9A, the first semiconductor substrate 10A andthe second semiconductor substrate 10B are bonded with each other usingthe aforementioned plasma bonding and the like. Subsequently, as shownin FIG. 9B, the edge of the first semiconductor substrate 10A that maycause damage to the surface of the second semiconductor substrate 10B isleft as it is, and the internal region 10 a in which devices such as theMOS transistors Tr are formed is ground. Afterward, the internal region10 a is thinned as deep as a predetermined film thickness using a wetetching method.

Next, as shown in FIG. 9C, the edge of the first semiconductor substrate10A is removed using an edge trimming method.

It is to be noted that before or after the bonding of the firstsemiconductor substrate 10A and the second semiconductor substrate 10B,as with the above-described first to third embodiments, a protectivefilm such as an SiN film may be provided over the whole surface or atthe edge of the second semiconductor substrate 10B. Such a manner makesit possible to suppress mechanical damage of the surface of the secondsemiconductor substrate 10B that may be caused by broken pieces inremoving the edge of the first semiconductor substrate 10A.

As a currently-available method of removing an edge of an upper-layersubstrate after the bonding of the upper-layer substrate and alower-layer substrate, there is, for example, a method disclosed inJapanese Unexamined Patent Application Publication No. 2008-84976 inaddition to the removal method disclosed in the aforementioned PatentGazette (Japanese Unexamined Patent Application Publication No.2011-96851, and the like). More specifically, a circular convex portionis formed at a peripheral region surrounding a device formation regionby performing a grinding process by the use of a first grind stone, andthereafter a whole backside of an upper-layer substrate including thecircular convex portion is ground to be flattened using a second grindstone with an abrasive grain diameter smaller than that of the firstgrind stone. Although this method makes it possible to prevent theupper-layer substrate from being processed like a knife edge, it may bedifficult to avoid occurrence of damage of the lower-layer substratethat may be caused by direct striking of broken pieces of theupper-layer substrate in a second grinding process. As a result, metalelution due to a subsequent chemical liquid treatment or contaminationdue to dust generation may occur.

On the contrary, in this embodiment, in a thinning process of the firstsemiconductor substrate 10A, the edge is left as it is, and the internalregion in which devices are formed is mechanically ground. Subsequently,the substrate 11A is further thinned as deep as a predeterminedthickness with the edge left as it is by performing a chemical treatmentusing chemical liquid, and thereafter the edge of the firstsemiconductor substrate 10A is removed using the edge trimming method.By going through such a process, it is possible to prevent metal elutiondue to a subsequent chemical liquid treatment or contamination due todust generation.

6. Application Examples

The image pickup device 1 including a semiconductor device that isformed using any of the manufacturing methods described in theaforementioned first to fourth embodiments is applicable to varioustypes of electronic apparatuses having photographing functions,measuring functions, display functions, and the like. As describedabove, the image pickup device 1 is capable of providing high-qualitycolor images, and thus it is preferred for mobile apparatuses, such as acamera (digital still camera or video camera), or a mobile phone and aPDA (Personal Digital Assistant) having photographing functions. Inaddition, the image pickup device 1 is also applicable to a specificsubstance measuring (detecting) apparatus, and the like. As an example,FIG. 10 shows a functional block configuration of a camera (camera 200).

The camera 200 is provided with an optics system including a lens group231, the image pickup device 1, a DSP circuit 232 that serves as acamera signal processing section, a frame memory 235, a display unit233, a recording unit 236, an operational system 234, a power supplysystem 237, and the like. Among these component parts, the DSP circuit232, the frame memory 235, the display unit 233, the recording unit 236,the operational system 234, and the power supply system 237 areconfigured to be interconnected with one another via a bus line 238.

The lens group 231 acquires incident light (image light) from aphotographic subject to form an image on an imaging surface(light-receiving surface) of the image pickup device 1, and isconfigured of one or more lenses. The image pickup device 1 outputsimage pickup data D0 on the basis of the incident light that is imagedon the imaging surface by the lens group 231. The display unit 233 maybe configured of, for example, a liquid crystal display unit or anorganic EL (Electroluminescence) display unit, and the like, anddisplays moving images or still images (color images for which imageprocessing has been completed by an image processing section 22) thatare photographed by the image pickup device 1. The recording unit 236records the moving images or still images that are photographed by theimage pickup device 1 on a recording medium, such as a video tape and aDVD (Digital Versatile Disk). The operational system 234 functions as anexternal signal input means in response to the user operation, andreceives operational commands concerning various functions provided bythe camera 200 to send these commands to internal circuits. The powersupply system 237 includes various power supplies that serve asoperation power supplies for the DSP circuit 232, the frame memory 235,the display unit 233, the recording unit 236, and the operational system234.

The present disclosure is described thus far with reference to someembodiments and modification examples. However, the present disclosureis not limited to the above-described embodiments, and variousmodifications may be made. For example, in the above-describedembodiments and the like, as an image sensor, a CMOS image sensor of abackside illumination type or a front-side illumination type is taken asan example. However, the image sensor is not limited to such a CMOStype, and a CCD (Charge-Coupled Device) image sensor, or a MOS imagesensor may be also acceptable.

It is to be noted that the present technology is allowed to have theconfigurations described following (1) to (15).

(1) A method of manufacturing a semiconductor device, the methodincluding:

bonding a device formation side of a first substrate having a firstdevice and a device formation side of a second substrate having a seconddevice in opposition to each other;

forming a protective film on at least an edge of the second substratehaving the second device; and

reducing a thickness of the first substrate.

(2) The method according to (1), further including:

forming a thinned portion at an edge of the second substrate prior tobonding of the first substrate and the second substrate; and forming theprotective film on a side surface of a device on the second substratethat is exposed by formation of the thinned portion and on a surface ofthe thinned portion.

(3) The method according to (1) or (2), further including: smoothing andcleaning a surface of the second substrate after forming the thinnedportion on the second substrate.

(4) The method according to any one of (1) to (3), further including:forming a thinned portion at an edge of the first substrate; andreducing a thickness of a whole surface of the first substrate afterremoving the thinned portion.

(5) The method according to any one of (1) to (4), wherein theprotective film is formed over a whole surface of the first substrate.

(6) The method according to any one of (1) to (5), wherein theprotective film is formed of a material having chemical resistance.

(7) A method of manufacturing a semiconductor device, the methodincluding:

forming a thinned portion at an edge of a first substrate having a firstdevice;

forming a protective film that absorbs no laser beams on at least anedge of a second substrate having a second device;

bonding the first substrate and the second substrate with the firstdevice and the second device opposed to each other; and

selectively removing the thinned portion of the first substrate using alaser.

(8) The method according to (7), further including: reducing a thicknessof a whole surface of the first substrate after removing the thinnedportion of the first substrate.

(9) The method according to (7) or (8), further including: using a lasermicrojet to remove the thinned portion of the first substrate.

(10) The method according to any one of (7) to (9), further including:forming the protective film over a whole surface of the second substrateprior to bonding of the first substrate and the second substrate.

(11) A method of manufacturing a semiconductor device, the methodincluding:

bonding a first substrate having a first device and a second substratehaving a second device with the first device and the second deviceopposed to each other;

reducing a thickness of an internal region excluding an edge of thefirst substrate; and

removing the edge of the first substrate.

(12) The method according to (11), further including: forming aprotective film at an edge of the second substrate after bonding of thefirst substrate and the second substrate.

(13) The method according to (11) or (12), further including: bondingthe first substrate and the second substrate after forming a protectivefilm over a whole surface of the second substrate.

(14) The method according to any one of (11) to (13), further including:reducing a thickness of an internal region of the first substrate usinga mechanical grinding process.

(15) The method according to any one of (11) to (14), further including:reducing a thickness of an internal region of the first substrate usinga chemical treatment.

This application claims the priority on the basis of Japanese PatentApplication No. 2012-007086, No. 2012-007087, and No. 2012-007088 filedon Jan. 17, 2012 in Japan Patent Office, the entire contents of whichare incorporated in this application by reference.

Those skilled in the art could assume various modifications,combinations, subcombinations, and changes in accordance with designrequirements and other contributing factors. However, it is understoodthat they are included within a scope of the attached claims or theequivalents thereof.

The invention claimed is:
 1. A method of manufacturing an image sensordevice, the method comprising: providing a first substrate havingthereon a first device layer and a second substrate having thereon asecond device layer, the first device layer containing pixel circuitryfor converting light into image signals, the second device layercontaining circuitry for processing the image signals, the firstsubstrate being wider than the first device layer in cross section so asto have an edge portion extending beyond an edge of the first devicelayer; bonding the first and second device layers to each other; forminga protective film on at least an edge of the second substrate; andforming a first thinned portion of the first substrate by reducing athickness of the first substrate at the edge portion.
 2. The methodaccording to claim 1, further comprising: forming a second thinnedportion at an edge of the second substrate prior to bonding of the firstdevice layer and the second device layer; and forming the protectivefilm on a side surface of an electronic device on the second substratethat is exposed by formation of the second thinned portion and on asurface of the second thinned portion.
 3. The method according to claim2, further comprising: smoothing and cleaning a surface of the secondsubstrate after forming the second thinned portion on the secondsubstrate.
 4. The method according to claim 1, further comprising:removing the first thinned portion; and reducing a thickness of a wholesurface of the first substrate after removing the first thinned portion.5. The method according to claim 1, wherein the protective film isformed over a whole surface of the first substrate.
 6. The methodaccording to claim 1, wherein the protective film is formed of amaterial having chemical resistance.
 7. A method of manufacturing animage sensor, the method comprising: providing a first substrate havingthereon a first device layer and a second substrate having thereon asecond device layer, the first device layer containing pixel circuitryfor converting light into image signals, the second device layercontaining circuitry for processing the image signals, the firstsubstrate being wider than the first device layer in cross section so asto have an edge portion extending beyond an edge of the first devicelayer; forming a thinned portion at the edge portion of the firstsubstrate; forming a protective film that absorbs no laser beams on atleast an edge of the second substrate; bonding together the firstsubstrate and the second substrate with the pixel circuitry and thelogic circuitry opposed to each other; and selectively removing the edgeportion of the first substrate using a laser.
 8. The method according toclaim 7, further comprising: reducing a thickness of a whole surface ofthe first substrate after removing the edge portion of the firstsubstrate.
 9. The method according to claim 7, further comprising: usinga laser microjet to remove the edge portion of the first substrate. 10.The method according to claim 7, further comprising: forming theprotective film over a whole surface of the second substrate prior tobonding of the first substrate and the second substrate.
 11. A method ofmanufacturing an image sensor, the method comprising: providing a firstsubstrate having thereon a first device layer and a second substratehaving thereon a second device layer, the first device layer containingpixel circuitry for converting light into image signals, the seconddevice layer containing circuitry for processing the image signals, thefirst substrate being wider than the first device layer in cross sectionso as to have an edge portion extending beyond an edge of the firstdevice layer; bonding together the first and second device layers withthe pixel circuitry and the logic circuitry opposed to each other;reducing a thickness of an internal region excluding the edge portion ofthe first substrate; and removing the edge portion of the firstsubstrate.
 12. The method according to claim 11, further comprising:forming a protective film at an edge of the second substrate afterbonding of the first and second device layers.
 13. The method accordingto claim 11, further comprising: bonding the first substrate and thesecond substrate after forming a protective film over a whole surface ofthe second substrate.
 14. The method according to claim 11, furthercomprising: reducing a thickness of an internal region of the firstsubstrate using a mechanical grinding process.
 15. The method accordingto claim 11, further comprising: reducing a thickness of an internalregion of the first substrate using a chemical treatment.